Devices as described above are generally known. One construction is for instance described in JP 58 117 954 in the name of Nara Machinery Company Ltd. In the apparatus, due to the absence of axial pitch in the gap, the product is mixed substantially in radial direction, as forces in axial direction are virtually absent. Transport in axial direction is not imposed by the paddles, but occurs under the influence of an external force, for instance under the influence of gravity upon inclined arrangement of the trough and/or by pressure differences resulting from continuous supply of product.
The paddles and/or the trough are arranged for being in heat exchanging contact with the product. In the apparatus, the product may be cooled, dried and/or heated, with use being made of radial mixing of the product.
In such an apparatus, per mixing shaft, all mixing paddles are placed in line in order to prevent axial forces by the paddles on the product as much as possible. A drawback of such a set-up is that peak load on the shafts and drive can occur. This is the case especially with products having a high density and/or viscosity, as for instance dehydrated sewage sludge.